The 20-year-old man was traversing rapids with a friend in the Wilmot River in the state's north on Sunday afternoon when he became separated from his kayak and was forced to swim downstream.

His friend made it to shore late on Sunday and raised the alarm but a helicopter search in darkness proved fruitless.

The man was spotted by air not long after first light on Monday and winched some 30 metres to safety from the side of a cliff in the gorge.

"(We) saw him clinging to rocks, waving for help," constable Josh Peach told reporters.

"He was on a steep rock corner of the river, in a position where he was unable to use the river to get any further north or south.

"He was certainly unable to climb out due to the steepness of the gorge."

Temperatures in the area dropped to below 1C overnight.

Constable Peach said the man was well-prepared and had dry underclothing but still would have experienced a difficult, cold and wet night.

Both kayakers were wearing safety equipment including life jackets and helmets, police say.

The man, from Tasmania's northwest was treated for mild hyperthermia.

Australian Associated Press